Iridium is a dense, corrosion-resistant metal used in specialized alloys and durable electrical contacts. A platinum-iridium alloy once provided the international meter bar. This history connects material stability to measurement standards, while iridium's demanding applications show why resistance to heat and chemical attack matters.
FROM ELEMENT TO APPLICATION
AN ELEMENT IN CONTEXT
Why place iridium at a spark-plug tip instead of making the entire plug from it?
Iridium-containing spark-plug tip
FOLLOW THIS RELATIONSHIP
Locate the demanding interface
A spark-plug electrode tip repeatedly participates in an electrical discharge. That small region experiences demanding local conditions and must retain a useful working surface.
Explore the model (optional)
IrFORM → INTERACTION → CONSEQUENCE
Follow the explanation in either direction. These are authored steps, not a physical clock.
Optional: check your understanding
USE THE EXPLANATION
What is the best reason a small iridium-containing tip can be useful?
Atomic identity, reference properties and structure models
INTERACTIVE 3D77 visible sites
An electron censusDrag to rotate · scroll or pinch to zoom
[Xe] 4f14 5d7 6s2. Grouping electrons by principal shell connects the neutral-atom configuration to periodic-table patterns.
What this representation means
A three-dimensional counting diagram. Dots are count markers, not measured electron positions; spherical placement and spacing are arbitrary. There are no electron trajectories here. Orbitals describe quantum states.
Smithson Tennant identified iridium together with osmium in 1803 while studying residue from platinum processing. Its name refers to the colors of its compounds. In 1889, a platinum–iridium bar became the international prototype defining the meter. The connection joins discovery chemistry to metrology: a material first distinguished through reactive separations later helped preserve a reproducible physical length for comparisons between laboratories.
1803
Iridium identified
Tennant distinguished iridium in platinum-processing residue.
1889
Meter prototype adopted
An international platinum–iridium length standard was sanctioned.
Iridium occurs with other platinum-group metals and can be present in natural . It is recovered from complex and streams, including those associated with nickel. A sparse concentration in a rock and a carefully prepared alloy standard are different stages, connected by chemical separation and materials manufacture.
Iridium is a hard, corrosion-resistant metal suited to demanding surfaces and alloys. Its colored salts demonstrate that elemental appearance does not predict every compound's color. A spark-plug tip and a historical measurement bar exploit durable metallic material, whereas the optical clues in its discovery belonged to compounds.
Each section links its supporting references. Descriptions and diagrams were authored for this atlas. Source checks completed. Source checks dated 2026-09-06.
CITE THIS PAGE
Family labels and the group-3 layout are teaching conventions. A table position does not establish an unknown bulk property. Electronic configurations refer to neutral atoms; ions and material environments require their own account.
Read each reference property together with its units, conditions and the reference information below.
Not yet recorded: electron affinity, second ionization energy, ground-state term symbol, van der waals radius, thermal conductivity, specific heat capacity, electrical resistivity, crystal structure, lattice parameter a, space group, abundance in seawater, abundance in the universe, annual production, supply-risk listing, hazard classification, biological role, cas registry number, pubchem cid, wikidata item. These families are declared and awaiting an ingestion run against the source each names; they are listed here rather than shown as empty rows.
Physical
Intended reference: CRC Handbook of Chemistry and Physics · CRC Press
Phase at 20 °C
solid
293.15 K, 101.325 kPa
Melting point in K
2719 K
at standard pressure unless noted
Boiling point in K
4403 K
101.325 kPa
Density in g/cm³
22.56 g/cm³
solids and liquids at 293 K; gases at 273 K and 101.325 kPa
Atomic and electronic
Intended reference: Pauling electronegativity scale · Widely tabulated; original in The Nature of the Chemical Bond
Electronegativity in Pauling
2.2 Pauling
Pauling scale
First ionization energy in kJ/mol
880 kJ/mol
gas-phase neutral atom, ground state
Covalent radius in pm
141 pm
single-bond covalent radius
Common oxidation states
+3, +4
states met in ordinary compounds; not exhaustive
Occurrence and identity
Intended reference: CRC Handbook of Chemistry and Physics · CRC Press
Abundance in the crust in mg/kg
0.001 mg/kg
upper continental crust, mass fraction
Has stable isotopes
Yesderived
Discovery year in CE
1803 CEderived
WHERE IT SITS AMONG ITS NEIGHBORS
Electronegativity across period 6
Ir 2.2 Pauling · Iridium
Electronegativity across period 6. Exact values.
Cs
0.79
Ba
0.89
La
1.1
Ce
1.12
Pr
1.13
Nd
1.14
Sm
1.17
Eu
1.2
Gd
1.2
Tb
1.1
Dy
1.22
Ho
1.23
Er
1.24
Tm
1.25
Yb
1.1
Lu
1.27
Hf
1.3
Ta
1.5
W
2.36
Re
1.9
Os
2.2
Ir
2.2
Pt
2.28
Au
2.54
Hg
2
Tl
1.62
Pb
2.33
Bi
2.02
Po
2
At
2.2
Electronegativity down group 9
Ir 2.2 Pauling · Iridium
Electronegativity down group 9. Exact values.
Co
1.88
Rh
2.28
Ir
2.2
The trend uses the same reference-property values as the periodic table. Elements with no recorded value are left out of the line rather than drawn at zero.
